45. From the passage we learn that

　　[A] an invention will not benefit the inventor unless it is reduced to commercial practice

　　[B] products are actually inventions which were made a long time ago

　　[C] it is much cheaper to buy an old patent than a new one

　　[D] patent experts often recommend patents to others by conducting a search through dead patents

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　　[长难句突破]

　　A granted patent is the result of a bargain struck between an inventor and the state, by which the inventor gets a limited period of monopoly (垄断) and publishes full details of his invention to the public after that period terminates.

　　主体句式：A granted patent is the result of a bargain.

　　结构分析：本句的中心词就是“bargain”，“struck between an inventor and the state”指出bargain的双方身份，而后面的by which引导的从句具体说明了bargain的内容。

　　Because a patent remains permanently public after it has terminated, the shelves of the library attached to the patent office contain details of literally millions of ideas that are free for anyone to use and, if older than half a century, sometimes even re-patent.